This invention relates to a fluid-operated striker assembly which has a striker piston movable in a working cylinder and adapted to strike a tool bit as well as a control system having a control plunger movable in a control valve. The striker piston has two piston faces of different sizes. The smaller piston face is effective in the direction of the return stroke and is continuously connected with a pressure conduit in which working pressure prevails. The larger piston face is effective in the direction of the working stroke (forward stroke) and is alternatingly connected by the control valve with the pressure conduit and with a depressurized return conduit. The control plunger has two control faces of different sizes, operating in opposite directions. The smaller control face which is effective in the direction of the return stroke position of the control plunger is continuously connected with the pressure conduit whereas the larger control face is, by means of a circumferential groove situated between the piston faces, alternatingly and only for certain periods connected with the pressure conduit and the depressurized return conduit.
A striker assembly of the above-outlined type is disclosed, for example, in German Patent No. 3,443,542 to which corresponds U.S. Pat. No. 4,646,854 issued Mar. 3, 1987. By using a particular holding or switching valve which is incorporated in the control conduit cooperating with the control system and which is alternatingly also connected with the return conduit, it is sought to be ensured that even in case of a reflection of the striking energy from the tool bit to the striker piston, such reflected energy is hydraulically regained whereby an increase of the striking frequency of the striker piston is achieved.
Fluid-operated striker assemblies, particularly hydraulic hammers, are generally used for breaking up rocks or concrete. For such an operation the kinetic energy of a striker piston is transmitted to the tool bit by delivering blows thereto by the striker piston, and the kinetic energy is converted to comminuting work at the tool bit tip. In case of relatively hard materials, only one part of the kinetic energy is converted to comminuting work, dependent upon the hardness of the material to be comminuted. The unconverted energy portion is reflected by the tool bit to the striker piston and may be used, with a suitable device, to increase the striking frequency. In contrast, in case of relatively soft materials, the striking (kinetic) energy is fully converted to comminuting work. The softer the material the greater the comminuting effect of the tool bit and the deeper the penetration of the tool bit into the material.
Processes in which the applied striking energy is higher than the energy required for the comminution are undesirable because of the resulting higher stresses on the striker assembly. The rapid adaptation of the striking energy to all operational conditions is a significant condition for a longer service life of the striker assembly and for an optimal comminution of material.